Stock market crashes are rare and destructive, and an article in Barron’sreexamines the red flags leading up to 1987’s Black Monday crash, when the Dow plummeted 507.99 points, a record 22.61% in a single day.

Some possible culprits for the crash included portfolio insurance, a new type of automated trading that bought futures when stocks went up and sold them when stocks went down, and an increase in interest rates, as well as a disappointing trade-deficit report and an unfavorable tax proposal in the House at the time.

Regardless of what caused it, the article continues, the result was panic. But the real mystery is that what followed the one-day crash wasn’t a recession or a depression, as opposed to the first Black Monday in 1929. After a 3-month bear market, the Dow recovered within 2 years. Though Alan Greenspan, the Fed Chair at the time, is widely credited for fostering the recovery by pledging the central bank’s “readiness to serve as a source of liquidity,” that action alone can’t account for the calm that returned relatively quickly.

Perhaps the fascination with the 1987 crash continues because it was so inexplicable, which also makes it a bit frightening. Despite any warning signs, when a crash comes, it’s usually a surprise, something worth remembering in the current climate.